l. FIELD OF THE INVENTION
The present invention relates generally to the reduction of power plant acid rain emissions, and to the conservation and recovery of wasted energy.
2. DESCRIPTION OF THE PRIOR ART
Approximately 50% of the electric utility power produced in the United States is generated by coal fired power plants. Even low-sulfur-content coal, fed to fire the plant, emits sulfur dioxide vapors which substantially contribute to the phenomenon known as acid rain. The flue gases containing such acid rain vapors are discharged from the power plants at temperatures as high as between 400 and 450 degrees F. Otherwise, the flue gases would condense in the stack causing corrosion problems. Accordingly, methods to inhibit acid rain by cooling and condensing the acid vapors in a non-corrosive manner are essential.
The conventional means for chemical absorption processes or by cooling such flue gas and condensing the hazardous vapors by use of water scrubbers and off-site waste water holding lagoons. However, chemical solids waste and waste water holding lagoons create an environmental nuisance. That is, hazardous chemicals leak into natural water streams. Additionally, the scrubbers and the lagoon water systems are very expensive to install, operate and maintain. An additional drawback is that the heat content of the flue gases, 6 which may amount to as much as 15% of the energy employed in the plant, is routinely wasted during the scrubbing operations.
A further loss of energy occurs in exhausting and/or condensing saturated steam from the steam turbine of electric power plants fired by the coal fuel. The steam loses its latent heat of evaporation to the cooling water as the water discharges its heat into the atmosphere or finds its way into natural water streams.
In the past, attempts have been made to recover the waste heat from saturated steam, such as with a turbo generator device in U.S. Pat. No. 4,016,725; a vacuum apparatus in U.S. Pat. No. 3,760,871; and an expansion chamber in U.S. Pat. No. 4,109,470. However, such extraneous equipment is inefficient, cumbersome, unduly expensive, and plays no role in reducing acid vapor emissions from the plant.
An improved method for reducing acid vapor emissions in a non-corrosive manner, eliminating deleterious environmental hazards, and recovering the wasted energy from both the flue gases and condensing the steam, would serve to reduce the amount of coal fuel needed to generate each kilowatt hour of power generated from the plant and significantly improve the environment. Furthermore, the reduction of coal usage would reduce the amount of carbon dioxide discharged into the atmosphere per kilowatt hour and thus reduce the so called "greenhouse warming potential" of existing facilities.
Previous methods for reducing emissions from flue gases by scrubbing the waste gases and cooling the flue gases through 6 expansion in turbine devices are disclosed in U.S. Pat. No. 3,854,300, but fail to efficiently conserve energy and serve to merely displace rather than reduce the environmental problem. Previous separation of water vapor from the gas stream by absorption, such as in U.S. Pat. No. 4,265,088, does not allow recovery of waste energy, and cooling the flue gas to separate the water vapor by the direct expansion (throttling) refrigeration method disclosed in U.S. Pat. No. 4,227,647 has also proven ineffective.
In the past, those attempts made to conserve waste energy from boiler flue gases by converting such energy into useful work have been limited to high temperature (over 500 degrees F.) flue gas economizers that produce high pressure steam to drive steam turbines. Unfortunately, when flue gas emissions are below 500 degrees F. there is insufficient energy to economically produce steam at the temperatures and pressures needed to drive the steam turbine.
U.S. Pat. Nos. 3,699,777 and 4,010,378 disclosed electric generation and space conditioning systems which utilized vapor generators to vaporize motive fluid to drive a multivaned rotary expander or compressed air to drive a turbine. The object was to provide electric power and space heating to mobile living quarters such as campers, trailers, boats and remote buildings. However, such systems can not be employed with toxic acidic vapor emissions from a power plant and the vaporized motive fluid is not condensed and recycled.
The present invention fulfills the long felt need in the industry for reduction of emissions and conservation of energy while overcoming the waste water lagoon/scrubber drawbacks in the prior art.